Im putting together my 3rd member 489 case soon and I'm in the process of buying the parts. I was wanting to run a detroit locker diff, but I am having a hard time finding on for a 489 case, only 742's Im seeing. Im open to different differentials, so what are you guys using or is there a detroit locker for a 489 that I am not seeing for sale online.

Any differential from any 8 3/4 will work in any other housing, as long as you use the bearings that match. So a Detroit Locker that fits a 742 will fit a 741 will fit a 489 will fit a 657, etc.
The major difference between these different housings is the configuration of the pinion and bearings.
www.doctordiff is a Board member who does this for a living. Ask him.

R.